The invention relates to a method and apparatus for transferring pressurized liquefied gas from one storage container to another. Specifically, a portion of vaporized liquefied gas occurring above the liquefied gas in a storage container is used to drive an air motor which in turn drives a pump that transfers the liquefied gas from one storage container to another storage container. Further, the apparatus of the invention may be mounted on a tank truck and used to transfer liquefied gas into or out of the tank truck storage container.
Liquefied gases are used for many diverse purposes in industry. Typically these gases are stored in a liquid state and must be transported from one location to another.
For example, carbon dioxide may be obtained from industrial processes, liquefied and stored in containers at one location. The liquid carbon dioxide may then be transferred to a tank truck in liquid form and transported to another location or plant where the liquid carbon dioxide may be used in industrial processes. The liquid carbon dioxide must therefore be transferred from a first storage container to the tank truck, and when it reaches its final destination it must be transferred from the tank truck to another storage container.
Typically fuel powered motors are used in conjunction with pumps to transfer liquefied gases such as liquid carbon dioxide from a tank truck to a storage container or from a storage container to a tank truck. The fuel powered motor and pump are usually mounted on the tank truck.
As an alternative to fuel powered motors, electric powered motors have been used to drive the pump for transferring liquefied gases. The electric powered motor and pump are usually mounted on the tank truck, and the electric power must be supplied by an external source at the location where the liquefied gas is transferred.
Electric or fuel powered motor systems for transferring liquefied gases to or from tank trucks have several disadvantages. Electric or fuel powered motors present safety risks in many locations where liquefied gases must be transferred to or from a tank truck. For example, in many industrial plants the possibility of flammable vapors exists, and an electric powered motor represents a potential ignition source for these flammable vapors due to electric sparks. Likewise, a fuel powered motor may have hot surfaces that would ignite flammable vapors or it may have an electric ignition system that would generate electric sparks. In fact, many industrial plants have strict rules either prohibiting the use of electric or fuel powered motors in certain areas or requiring very strict procedures for the use of electric or fuel powered motors in those areas.
Fuel or electric powered motors also have the disadvantage of needing frequent maintenance which results in expense and prevents the tank truck from being used while the maintenance is performed.
Further, fuel powered motors are bulky and their weight decreases the payload of liquefied gas that a tank truck can carry. Fuel powered motors have the added disadvantage that fuel must be carried on the tank truck to operate them. Likewise, this fuel is an extra weight that decreases the payload of liquefied gas that the tank truck can carry, and also represents an added expense due to the cost of the fuel.
Fuel powered motor systems for transferring liquefied gases also have the disadvantage that they can only transfer liquefied gases from a tank truck to a storage container and not from the storage container to the tank truck. This limitation is a result of the non-reversibility of fuel powered motors.